Field of the Invention
The present invention relates to an image reading apparatus configured to read an image formed on an original (hereinafter referred to as “original image”) and an image reading method thereof.
Description of the Related Art
An image reading apparatus configured to read an original image, while moving a reading unit in a sub-scanning direction with respect to an original placed on an original table, can detect a size of the original based on the read original image. For example, the image reading apparatus detects an original edge (original end portion) from the read original image to determine the original size based on a result of the detection. In this detection method, when dust, hair, or other dirt adheres to the original table or an original pressing member mounted to a back surface of a platen, the dust, hair, or other dirt may be falsely detected as the original edge. An image reading apparatus of Japanese Patent Application Laid-open No. 2001-36696 determines whether each pixel of the read image is an original region candidate pixel or an original region outside candidate pixel to detect the original edge based on the number of continuous candidate pixels.
In the image reading apparatus of Japanese Patent Application Laid-open No. 2001-36696, the original pressing member provided to the platen has a black color on the original table side. Alternatively, the image reading apparatus of Japanese Patent Application Laid-open No. 2001-36696 is based on a premise that the original is read with the platen kept open. In this manner, a luminance of a region outside the original region is decreased, and thus the determination between the original region candidate and the original region outside candidate is facilitated. However, such an image reading apparatus is required to change the original pressing member, which normally has a white color on the original table side. Alternatively, when the original is read with the platen kept open, a user may feel dazzled due to a light source irradiating the original with light.
The present invention has been made in view of the above-mentioned problems, and has an object to provide an image reading apparatus capable of detecting an original size with high accuracy while an influence of dirt is suppressed without the need to replace an original pressing member or read an original with a platen kept open.